Ruthenium-Catalyzed Dimerization of 7‑Oxabicyclo[2,2,1]hepta-2,5-diene-2,3-dicarboxylates

The ruthenium catalyzed dimerization of oxanorbornadiene dicarboxylates was studied. The effects of the ester moiety and the addition of a C1 substituent to the bicyclic alkene on the reaction were explored, and moderate yields and excellent regioselectivities were obtained

Type 1 Ring-Opening Reactions of Cyclopropanated 7‑Azabenzonorbornadienes with Organocuprates

The first nucleophilic ring-opening reactions of cyclopropanated 7-azabenzonorbornadienes have been achieved using organocuprates. Tricyclic or tetracyclic γ-lactams were obtained as the sole product in good yields of up to 98% when alkoxycarbonyl groups occupied the N-substituent position. Successful conversions to lactams were observed for primary, secondary, tertiary, and aromatic nucleophiles, as well as for a variety of substrates functionalized on the benzene ring. A possible mechanism for these transformations is discussed

Study on the Regioselectivity of Rhodium-Catalyzed Ring Opening Reactions of C₁-Substituted 7-Oxabenzonorbornadienes with Boronic Acids

<div><p></p><p>An optimized condition for the rhodium-catalyzed ring-opening reaction of C₁-substituted oxabicyclic alkenes with aryl boronic acids was developed and the effect of aryl boronic acid as well as the effect of C₁ substitution on the oxabicyclic alkenes was studied. Aryl boronic acids carrying electron-donating substituents provided the ring-opened products in excellent yields regardless of the position, while electron-withdrawing substituents were more susceptible to steric interactions. Although two different regioisomers are possible, all the rhodium-catalyzed ring-opening reactions of C₁ substituted oxabicyclic alkenes studied with aryl boronic acids were found to be highly regioselective, giving single regioisomers in all cases.</p></div

Synthesis of Cyclopropanated [2.2.1] Heterobicycloalkenes: An Improved Procedure

<div><p></p><p>A safer and improved method to our previous report on palladium-catalyzed cyclopropanation of heterobicyclic alkenes has been developed. By using THF as the solvent and a more dilute aqueous NaOH solution for the generation of diazomethane from Diazald®, cyclopropanation could be achieved smoothly with minimal adjustment over the course of reaction. 7-Oxabicyclic substrates with bulky C1 or C2 groups, as well as 2,3-diazabicyclic substrates with various N-substituents effectively underwent cyclopropanation. Using this methodology, yields to previously reported products were markedly increased, and 10 new cyclopropanated [2.2.1] heterobicyclic products were prepared. In addition, this work accounts for the first reported cyclopropanation of 2,3-diazabicyclic alkenes, which all gave excellent yields of >90%.</p></div

Iridium/Zinc-Co-Catalyzed Ring-Opening Reactions of Oxabicyclic Alkenes with Indole Nucleophiles: A Combined Experimental and Theoretical Study

An experimental and theoretical investigation on the iridium/zinc-co-catalyzed ring-opening reactions of oxabicyclic alkenes with indole nucleophiles is reported. The reaction affords trans-3-indolyl-1,2-dihydronaphthalen-1-ol products in good yield with no N-alkylated products observed. The C–C bond-forming reaction does not require prior functionalization and is entirely atom-economic. The mechanism and origins of selectivity in the iridium-catalyzed ring-opening reaction have been examined at the M06-D3/Def2TZVPP level of theory. Orbital analysis and natural population analysis charges demonstrate that the Cα site of the π-allyliridium intermediate is the most electrophilic site of attack. Distortion/interaction analysis reveals that the chemoselectivity likely originates from an earlier-stage transition state between Cα and C3, which requires less distortion energy compared to Cα–N1 during the rate-determining intermolecular nucleophilic attack. Moreover, conceptual density functional theory was used to conceptualize the preferential reactive sites of the nucleophiles probed. The C–C bond-forming step is speculated to proceed through a Friedel–Crafts-type reaction

Iridium/Zinc-Co-Catalyzed Ring-Opening Reactions of Oxabicyclic Alkenes with Indole Nucleophiles: A Combined Experimental and Theoretical Study

An experimental and theoretical investigation on the iridium/zinc-co-catalyzed ring-opening reactions of oxabicyclic alkenes with indole nucleophiles is reported. The reaction affords trans-3-indolyl-1,2-dihydronaphthalen-1-ol products in good yield with no N-alkylated products observed. The C–C bond-forming reaction does not require prior functionalization and is entirely atom-economic. The mechanism and origins of selectivity in the iridium-catalyzed ring-opening reaction have been examined at the M06-D3/Def2TZVPP level of theory. Orbital analysis and natural population analysis charges demonstrate that the Cα site of the π-allyliridium intermediate is the most electrophilic site of attack. Distortion/interaction analysis reveals that the chemoselectivity likely originates from an earlier-stage transition state between Cα and C3, which requires less distortion energy compared to Cα–N1 during the rate-determining intermolecular nucleophilic attack. Moreover, conceptual density functional theory was used to conceptualize the preferential reactive sites of the nucleophiles probed. The C–C bond-forming step is speculated to proceed through a Friedel–Crafts-type reaction

Type 1 Ring-Opening Reactions of Cyclopropanated 7‑Oxabenzonorbornadienes with Organocuprates

For the first time, nucleophilic ring-openings of cyclopropanated 7-oxabenzonorbornadiene were investigated, providing a novel approach to the preparation of 2-methyl-1,2-dihydronaphthalen-1-ols. Satisfactory yields (up to 95%) were achieved using <i>n</i>-Bu₂CuCNLi₂ as the nucleophile and Et₂O as the solvent. The reaction demonstrated successful incorporation of primary, secondary, tertiary and aromatic nucleophiles, as well as ring-openings of substrates bearing arene substituents and C1-bridgehead substituents. A generalized mechanism for these transformations is also proposed

Ruthenium-Catalyzed Asymmetric [2 + 2] Cycloadditions between Chiral Acyl Camphorsultam-Substituted Alkynes and Bicyclic Alkenes

Ruthenium-catalyzed asymmetric [2 + 2] cycloadditions between chiral acyl camphorsultam-functionalized alkynes and bicyclic alkenes were examined, providing adducts with complete <i>exo</i> stereoselectivity in good overall yield and enantioselectivity (up to 99% and 166:1, respectively), as well as appreciable diastereoselectivity (up to 163:1). The diastereoselectivity showed dependence on the solvent and temperature, as well as on the substitution pattern of the reacting alkyne and bicyclic alkene components. In general, higher diastereoselectivities were observed for reactions conducted in ethereal solvents and at lower temperatures between <i>N</i>-propynoyl camphorsultams and bicyclic alkenes

Ruthenium-Catalyzed [2 + 2] Cycloadditions between Norbornene and Propargylic Alcohols or Their Derivatives

Diastereoselective ruthenium-catalyzed [2 + 2] cycloadditions of norbornene and propargylic alcohols or their derivatives were investigated. The cycloadditions were found to be highly stereoselective, giving exo cycloadducts in moderate to excellent yields with diastereoselectivities up to 92:8. When a chiral propargylic alcohol was used in the cycloaddition, up to 80% ee of the [2 + 2] cycloadducts was observed after oxidation of the alcohol